I have an older used sand filter, and a new pump hooked up to my above ground pool. We are just setting this up and cannot get it to backwash. We replaced the sand thinking that might be the problem. No luck. It has a plunger type handle at the top that says "pull out to backwash and run for at least 2 minutes". When we pull it out and then start the pump it acts as it it sucks the water back up the waste hose for a second then nothing. If we then shut it off and push it back in and restart the pump, it circulates the water just fine, we can see it go into the pump and then into the pool. Does anyone have an idea what is going wrong here? Please help me get this going before it is 90 degrees outside